Tire assembling and vulcanization

ABSTRACT

A module (1) used for the manufacture of tires, comprising an inflatable flexible bladder (10) provided with two beads (11) which is used for the assembling and vulcanization of the tire on the bladder, each bead being anchored on a plate (30, 31). The module (1) has at least one rigid wall mounted on a plate (30, 31) which is adjacent said flexible bladder (10) when the latter is inflated and can be retracted so as to be able to separate the tire from said module (1) after vulcanization and can be spread out radially so as to constitute a reference surface for the assembling of the tire.

This application is a continuation of application Ser. No. 08/449,419,filed on May 24,1995, now abandoned.

BACKGROUND OF THE INVENTION

The present invention relates to the manufacture of tires. Moreparticularly, it relates to techniques for the manufacture of tires on asupport the shape of which is very close or even identical to the finalmanufactured shape of the tire.

U.S. Pat. No. 4,895,692 describes a tire mold having a rigid core whichdetermines the inner shape of the tire; it also describes a process ofassembling the tire with the use of such a mold. Such a mold can beconsidered "rigid", since this mold imposes upon the tire a moldingspace of a given volume. This volume is bounded on the outside by theshells of the mold and by the group of sectors molding the tread, and onthe inside by the rigid core. The use of this mold leads to avulcanization stage with quasi-imposed volume. It is also known thatmost of the molds currently used at the present time are molds havingonly the two shells which assure the molding of the outside of thesidewalls and a ring of sectors which assure the molding of the outsideof the tread. The use of these molds upon vulcanization leads, in orderto assure the molding, to the spreading out within the raw tire of aflexible bladder, so that it can be considered that the vulcanizationtakes place in this case with imposed pressure and not with imposedvolume.

SUMMARY OF THE INVENTION

The object of the present invention is to manufacture a tire on asupport which is as close as possible to its final manufactured shape,in accordance with the technique described in U.S. Pat. No. 4,895,692,while carrying out a vulcanization step which is related rather to theprocess which has been referred to above as vulcanization with imposedpressure.

One object pursued by the invention is to create a process for themanufacture of a tire which avoids the tire blank undergoing, during itsassembly, transfers consisting in displacing it from one drum to anotheror one support to another. All such transfers and manipulations of theblank are in fact the source of numerous inaccuracies in assembly andthe source of defects in the uniformity of the tire produced.

For this purpose, the invention proposes a process for the manufactureof a tire which comprises an assembly phase forming a raw blank and avulcanization phase, in which use is made of an inflatable flexiblebladder capable of retaining by adherence the raw rubber constitutingthe inner skin of the tire during the assembly phase and capable ofseparating from the tire after vulcanization, which comprises thefollowing stages:

said bladder is inflated to a given assembly pressure so as to form areference support for the assembling, said support having a toroidalshape,

thereupon a raw blank is formed, starting by the depositing of therubber constituting the inner skin of the tire by the winding of aribbon, and then progressively depositing all the desired components, inthe required order, onto said bladder,

the blank is then vulcanized,

and finally said bladder is deflated and withdrawn from the inside ofthe tire.

In order to effect the vulcanizing of the blank on the bladder itself,there can advantageously be closed around the blank a mold for themolding of the outer surface of the sidewalls and the tread, and thepressure of said bladder then adjusted to a molding pressure which issufficient to assure the molding of the tire and, at the end of thevulcanization, the bladder is deflated in order to permit the separationof the skin and said bladder and to permit the discharge of thevulcanized tire.

This consists in manufacturing a tire completely on an inflatablebladder and then vulcanizing it on the same bladder, without anytransfer of the blank with respect to the bladder. The bladder used iscapable of maintaining the raw rubber constituting the inner skin of thetire upon the depositing during the assembly phase. It is understood bythis that the rubber ribbon which is deposited on the bladder adheres tothe latter sufficiently in order to remain in the place where it hasbeen deposited. For the depositing of this ribbon, one can use differenttechniques, such as the depositing of a preshaped ribbon, or else thedirect extrusion of an amount of rubber which is fully controlled as afunction of the exact place where it is deposited on the bladder.

It is furthermore necessary that the bladder used can separate from thetire after use. In order to satisfy these conditions, it is made of amaterial which makes it possible to obtain a good raw adhesive (that isto say, a material which the raw rubber adheres to sufficiently for therequirements of the depositing), while assuring the separation of thevulcanized tire. For example, the bladder is made of rubber having asurface covering which satisfies the conditions indicated. Aside formthe characteristic mentioned above, or in combination with it, one canalso use an elastomer which has a certain level of incompatibility withthe products used in the tire, and more particularly with the productsof which the inner skin of the tire is made.

By "manufacture of a tire", there is understood both complete andpartial manufacture, that is to say, possibly, the manufacture of a unitcomprising the crown reinforcements and the tread alone, or themanufacture of a tire without such a unit. Whatever the objectmanufactured, the reference support receives all the raw materials,which are in general deposited by winding on the support, as well as allthe following materials for producing a complete assembly, contrary toother known arrangements in which the vulcanization bladder or else areceiving drum such as a second-stage drum receives a complex productformed of a semi-finished product obtained by the assembling of severalelementary components.

By "support of toroidal shape", there is understood a support the shapeof the outer apparent surface of which is very far from a cylindricalshape, in order to approach a shape resembling the shape of the innersurface of the tire. This shape is therefore of a very different naturefrom the shape of the first-stage assembly drums known in the prior artwhich have a quasi-cylindrical surface, bordered on either side by agroove or a shoulder in order to define the position of the bead wires.This shape of revolution may have a radial section which isapproximately a circular arc or else resembling a trapezoid.

In order to be able to manufacture a tire on a form which correspondssubstantially to the final manufactured and vulcanized shape of thetire, a reinforced bladder is preferably employed. It is thus possibleto obtain a flexible form which, once inflated to a pressure of the sameorder of magnitude as the inflation pressure of passenger car tires,behaves substantially as a rigid form. This permits the use of tireassembly tools which are known for the manufacture of a tire on a rigidcore, such as those described in U.S. Pat. Nos. 4,801,344, and 4,804,436or else 4,963,207, by way of illustration but not of limitation.

The invention also proposes a tire manufacturing module which comprisesan inflatable flexible bladder which can be retracted when it isdeflated, said module comprising means making it possible to anchor saidbladder and making it possible to offer a hold for the displacement ofthe module and making it possible with said bladder to define aninflatable enclosure forming at least partially a support of toroidalshape in inflated state.

This module permits the assembling of a tire and its transfer then to avulcanization station. The module preferably has two connecting socketsmaking it possible to circulate a fluid providing the heat necessary forthe vulcanization. At the vulcanization station, the fluid used is, forinstance, electricity, the module being for instance equipped withresistors capable of producing heat, or else a heat-exchange fluid whichconducts heat to the inside of the module. As the case may be, saidconnecting sockets may be either electric inlets or connectors forgaseous or liquid fluid. Due to the sealing means between plates, itoffers the possibility of providing an autonomous inflated support whichcan be transported in inflated state from station to station during theassembling of the tire, without it being necessary to connect it eachtime to a source providing a fluid under pressure.

In accordance with one interesting embodiment, the invention offers amodule comprising a bladder provided with two beads, each bead beinganchored on a plate, said module comprising at least one rigid wallmounted on a plate, adjacent to said flexible bladder when it isinflated, arranged on the outer side thereof and retractable in order tobe able to separate the tire from said module after vulcanization andcapable of being spread out radially in order to constitute a continuoussurface serving as reference for the assembling of the tire.

The advantage of this arrangement is that it makes it possible moreeasily to effect the depositing of the rubber constituting the innerskin of the tire by the winding of a ribbon. One can, in fact, selectfor said wall a material onto which the first rubber windings adherevery easily, such as for instance a metal material. If the adjacentturns overlap slightly until covering the entire support, the adherenceof the ribbons to each other is sufficient in order for the rubberdeposited to be held in place on the support even if the rubber itselfadheres less easily to the bladder.

Preferably, said wall is extended radially up to a radius beyond whichthe radial section of the inner surface of the tire manufactured withsaid modules does not form any point of inflection. In this case,another advantage of the rigid wall associated with a bladder is that itmakes it possible to obtain a support on which a tire can bemanufactured really without any shaping due to the fact that in thiscase the support can correspond precisely to the inner shape of thetire.

The invention also covers a tire vulcanization station comprising a moldfor the molding of the outer surface of the sidewalls and tread of thetire, which is used with a module comprising an inflatable flexiblebladder capable of imparting a molding pressure to the inner surface ofa tire, said bladder comprising two beads, and said module havingfurthermore two plates each used for the anchoring of one of said beads,said module being mounted removably in the vulcanization station so thatit can be extracted from it or introduced into it and supporting a rawtire, said vulcanization station comprising means for assuring arelative axial movement between said plates when said module is mountedin the vulcanization station.

All of the operations for the configuration of the module (movements ofthe plates, adjustment of the inflation pressure of the bladder, etc.)which are necessary for the complete manufacture of the tire can becarried out in this vulcanization station. It comprises the means forconnecting the module to a source of fluid under pressure. The saidpressure can first of all be adjusted to that just necessary in order toeffect the assembling of the tire and then, when the module reaches thevulcanization station supporting a raw tire, it is possible to transmitto the module the pressure and the heat necessary for the vulcanization.Furthermore, it is also possible to impart to the module the movementsfacilitating the extraction of the bladder from the inside of the tireafter the vulcanization of the tire. It is, in fact, advantageous to beable to move apart the plates which support the bladder so as to cause afolding of the bladder. By combining this folding with a sufficientvacuum within the bladder, the bladder can be separated from the innersurface of the tire and folded in such a manner that the vulcanized tirecan easily be extracted.

Finally, the invention proposes a tire manufacturing machine comprisingan assembly unit and an associated vulcanization station. Moreprecisely, the manufacturing machine for a tire in accordance with theinvention comprises an inflatable flexible bladder capable of holdingthe raw rubber constituting the inner skin of the tire during theassembly phase and capable of separating from the tire after thevulcanization of the latter, and it comprises

at least one assembly station having the means necessary for forming araw blank,

at least one vulcanization station having the means necessary to assurethe curing of the blank, and

means for the transfer of said module between stations.

DESCRIPTION OF THE DRAWINGS

A non-limitative embodiment of the invention is described below withreference to the accompanying drawings. This makes it possible clearlyto understand the invention and all of its advantages.

FIG. 1 shows a tire manufacturing module in accordance with theinvention as configured for the assembling phase of a tire;

FIG. 2 is a partial side view, in the direction of the arrow II in FIG.1, of the same manufacturing module;

FIG. 3 illustrates a detail of the module, seen in the direction of thearrow III in FIG. 2;

FIG. 4 shows the same module during the vulcanization phase; and

FIG. 5 shows the module of the invention in the position for thedischarge of the tire.

DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 shows a flexible bladder 10 having two beads 11. Each of thebeads is mounted on a plate 30, 31. The bladder 10 has reinforcementwires 12 oriented 90° (in accordance with the customary convention forangles used in the tire industry), extending from one bead 11 to theother. The bladder 10 also has wires 13 which are oriented 0° . In ordernot to encumber the drawing, the arrangement of the wires 12 and 13 isindicated only locally. By the combination of these 90° wires and 0°wires, it is possible perfectly to control the profile in the convexportion of the outer surface of the bladder when it is inflated (that isto say, the contour of the radial section as shown above the points P inFIG. 1).

The plate 31 has a toroidal sealing joint 33 mounted in a groove whichis coaxial to said plate. The plate 30 has a shoulder 32 which comesagainst the sealing joint 33 when the two plates 30 and 31 are movedaxially against each other. The plate 31 comprises a locking mechanism34 which makes it possible to maintain the plates 30 and 31 connected.The locking mechanism 34 has several flexible blades 35 which arecircumferentially distributed and the end of which can engage in acircumferential groove 36 provided on the plate 30. The blades 35 areheld enclosed in the circumferential groove 36 by a nondeformable clip37 which can slide axially and is held in locking position against astop 38 under the action of a spring 39. In the assembled and lockedposition, the plates 30 and 31 form a rim 15 which, together with thebladder 10, constitutes an air-tight enclosure S capable of beinginflated due to an automatically closing valve 55 arranged on the plate31.

The module 1 formed in this manner is an independent unit which it ispossible to arrange at several places depending on the manufacturingrequirements of the tire. The plate 30 has an extension 16 which offersa grip by which the rim 15 can be grasped. In similar manner, the plate31 has an extension 17 offering a bearing surface by which the rim 15can be grasped.

In order to manufacture the bladder 10, one uses, for instance, aremovable or destructible rigid core which determines the shape of itsinner surface. On this rigid core, suitable rubber products aredeposited, such as, for instance, the elastomer HNBR (hydrogenatedacrylonitrile-butadiene rubber) or the elastomer ethylene acrylaterubber, or a fluorinated elastomer, and the reinforcement wires aredeposited, all in suitable manner. Thereupon, the assembly isvulcanized, using for instance an outer mold in order to impart thedesirable vulcanization pressure, or else using an autoclave.

The use of 90° wires and 0° wires, while it permits an excellent controlof the profile, does not, however, make it possible to obtain aninversion of the curvature of the support, that is to say it does notmake it possible to produce the concave portions of the outer surface ofthe manufacturing support of the tire. Stated differently, theinflection point P on the radial section of the bladder could not beobtained. In order to be able to come as close as possible to the finalinternal shape of a tire to be manufactured, there is preferablyemployed a rigid wall 4 which is arranged radially under the place Pwhere the section of the tire to be manufactured comprises a point ofinflection. The raw blank T of the tire to be manufactured is shown indashed lines, which makes it possible to see how it is arranged withrespect to the bladder 10 and with respect to the walls 4. In the eventthat such rigid walls 4 are used, the 0° wires can reinforce only theportion of the bladder 10 which is radially above the points ofinflection P. In such case, it is possible to completely control theshape of the radial section of the outer surface of the support on whichthe tire is manufactured without having to have recourse to otherartifices such as mechanical elements which are spread out within thebladder.

The construction of the rigid wall 4 is shown, in particular, in FIGS. 2and 3. It is necessary that this rigid wall 4 can be retracted when thetire is vulcanized in order to be able to release it from the module 1.For this purpose, the rigid wall 4 is formed by an assembly of/petal-like members 40 and 41. In spread-out position (FIGS. 1 to 4), themembers form a continuous surface, which can serve as reference for theassembling of the tire. The members are mounted on hinges 46 (see thebroken-away portion of FIG. 2 in particular), and can be folded back bya rotation which brings them towards the center of the module 1 (FIG.5). As this folding movement brings the radially upper part of thesemembers towards the smaller radii, the place which is circumferentiallyavailable decreases. It is therefore necessary that the members overlap,which is obtained in the case described by the fact that the members 40are folded back first and then only the members 41, so as to be arrangedstaggered, in retracted position, as is shown in FIG. 5. This movementwill be explained in detail below.

We note first of all that the position in which the members 40, 41define the rigid wall 4 is materialized by a stop 42 (see FIG. 1)against which the members 40, 41 rest via their extension 43. They areheld against this stop 42 by the inflatable bladder 10.

The edges 47 of the members 40 and 41 are oriented on a bias and formsupport faces which complement each other, as shown in FIG. 3. Eachwall, therefore, comprises an even number of members, distributed in twogroups (one group identified by the reference numeral 40 and a secondgroup identified by the reference numeral 41), the circumferentiallyadjacent members belonging to different groups. The bladder 10, notshown in FIGS. 2 and 3, is arranged on the side of the arrow M in FIG.3, and in the rear with respect to FIG. 2. The arrow M symbolizes theforce which the bladder 10 exerts under pressure against the membersleaves 40 and 41, which force places them against the stop 42. When thebladder 10 is deflated or placed under vacuum, the force against themembers 40 and 41 ceases. They are free to swing towards the positionshown in FIG. 5. This swinging movement takes place in the directionopposite the arrow M. As a result of the bias configuration of the sideedges 47, the swinging of the members 40 must always precede theswinging of the members 41, and the return against the stop 42 of themembers 41 must always precede the return of the members 40. Thestaggered arrangement of the members 40 and 41 is thus always possibleand no blocking can take place.

Springs 48 mounted on the members 40 and 41 develop a force whichopposes the force developed by the bladder 10 when the latter is underpressure. The force developed by these springs 48 therefore tendscontinuously to fold the members 40 towards the retracted configurationshown in FIG. 5. The movement from the retracted position of the membersto the outwardly extending position is controlled by the inflation ofthe bladder 10. The opposite passage is permitted by the deflating ofthe bladder 10. It is not necessary to provide a specific control forthe movements of the members. The springs 48 are arranged at least onthe side of the module 1 by which the vulcanized tire is discharged, fora reason which will be made clear in the following. However, nothingprevents equipping the two walls with identical springs.

FIGS. 4 and 5 show a module 1 mounted in a vulcanization station. Therecan be noted a mold for the molding of the outer surface of a tire,comprising two shells 57 and an assembly of sectors 58, as known per se.The vulcanization station comprises a gripper 50 on which the plate 31can be mounted, which plate is immobilized by spurs 500. A sealing joint52 mounted on the gripper 50 assures the tightness between the latterand the plate 31. A slide block 501 can push against the unlockingmechanism 34. A central piston-cylinder unit 51 is arranged at the levelof the axis of the mold. It engages the left-hand plate 30. Theconnection is effected at the level of the extension 16 by rockers 510,controlled by rod 511. A sealing joint 53 assures the seal between thecentral cylinder-piston unit 51 and the plate 30. Sealing means (notshown) are provided between the gripper 50 and the centralcylinder-piston unit 51. The assembly makes it possible to assure thetightness between plates 30 and 31 even when they are separated fromeach other.

The automatic closing valve 55, as well as another automatic closingvalve 56 which is slightly shifted circumferentially (see FIG. 2),constitute the inlet and outlet for a heat-exchange fluid which iscirculated within the bladder 10 at the vulcanization station. Thisheat-exchange fluid makes it possible to confer upon the bladder 10 thepressure necessary for the vulcanization, said pressure being in generalgreater than the molding pressure, and of course makes it possible toimpart to the tire the heat necessary for the vulcanization. Theconduits for the heat-exchange fluid and the circulation and heatingmeans for this fluid have not been shown in order not needlessly tocomplicate the drawings.

The manufacture of a tire can be effected in the following manner. Forexample, one can use a tire manufacturing machine having an assemblystation and a vulcanization station. In FIG. 1, there can be noted indot-dash line, a bracket 6 which supports the rim 15 on the left-handside, while on the right-hand side there can be noted a hub 7 on whichthe rim 15 is mounted.

The bracket 6 presents the module 1 to an assembly station comprising ahub such as 7. After mounting of the module 1 on the hub 7, the bracketreleases the module 1 and moves away. The module 1 is thus installed atthe assembly station and can be driven in rotation for the needs of thedepositing of the component products of the tire. One starts bydepositing onto the bladder 10 the butyl-base mix constituting the innerskin of the tire, whereupon all the necessary components are placedthereon, namely the reinforcement wires constituting the reinforcementof the tire and all the rubber mixes formulated in accordance with theplace where they are deposited, and therefore in accordance with thefunction of these rubbers in the tire. All the necessary components arethus deposited at the required place on said bladder. The object of thisinvention, not being the architecture of the tire itself, does notrequire the details concerning the construction of any particular tire.

After assembly of the blank T, a bracket 6 can again grasp the module 1,which is then freed from the hub 7 and transported from the assemblystation to the vulcanization station.

The use of the module 1 at the vulcanization station will now bedescribed, referring in particular to FIGS. 4 and 5. A bracket 6 (seeFIG. 1 for the bracket) brings the module 1 supporting a raw blank andpresents it to the gripper 50. The spurs 500 close around the rim 15.The bracket 6 releases the rim 15 and is evacuated. The centralcylinder-piston unit 51 approaches the plate 30 until engaging it. Therockers 510 grip the plate 30. The outer mold (shells 57 and sectors 58)can then be closed and all the operations for the curing of the tire canbe carried out.

Thereupon, the tire is removed from the mold, which starts with theopening of the outer mold. In order to retract the bladder 10 and swingback the members 40 and 41, the action of the vacuum within theenclosure defined by the bladder 10 is combined with an axial movementof relative separation of the plates 30 and 31. The slide block 501rests on the unlocking mechanism 34. From FIG. 5 it can be seen that thesliding of the central cylinder-piston unit 51 with respect to thegripper 50 makes it possible to move the plates apart. Due to thedifferent sealing joints, this enclosure remains air-tight, so that itis possible to place it under vacuum in order to favor the folding andmovement back of the bladder 10. One fold of said bladder 10 is visiblein FIG. 5. Air can also be injected under pressure between the tire andthe bladder 10 in order to facilitate the separation of the bladder. Afavorable point for this injection is the back of the members in theirradially upper part. An air channel 18 is provided within the thicknessof a member, debouching on the surface of the member, for instance at 14(see FIG. 4).

The tire can then be grasped by an unloading manipulator which grips itfor instance by the tread. It can be evacuated by relative axialdisplacement between tire and module. As the moving apart of the plates30, 31 precedes the discharging of the tire, it will be understood thatthe latter, which might have a tendency not to have followed themovement of the plate 30, must in all cases be capable of passingwithout difficulty over the assembly of members 40, 41 of the plate 30present on the evacuation side (left side in FIG. 5). It is thereforefrom this side alone that it is indispensable to prevent theirstraightening up and opposing the discharge of the tire. This is therole of the springs 48 in this embodiment.

Thereupon, the central cylinder-piston unit 51 brings the plate 30 backinto contact with the plate 31, whereupon the slide block 501 moves backin order to lock the plates and reconstitute the rim 15. In this way,the pressure inside the bladder can be reestablished to the levelsuitable for the assembling of the following tire.

The use of 0° and 90° wires of great stiffness (for instance of aramid)in order to reinforce a rubber bladder makes it possible nevertheless toretain for the latter an elastically deformable character under theeffect of the internal pressure while excellently controlling itsgeometry at a given pressure. One can thus have an assembly support ofvery good geometrical precision, which makes this support similar to therigid cores made of metal. At the same time, one has a vulcanizationbladder which is capable of very easily accommodating small variationsin the molding volume, due for instance to tolerances in the volumes ofrubber constituting the raw blank; one has a bladder which is capable ofaccepting a slight additional shaping which, if it is provided, makes itpossible to manufacture the raw blank very slightly below the final sizeof the tire, which can facilitate the closing of the sectors of themold, in particular with certain tread patterns. Even if such a bladder,during the molding starting the curing phase, transmits to the tire amolding pressure which is only a fraction of its inflation pressure, itnevertheless is similar to the non-reinforced bladders used currently upto the present time. The molding cavity which it defines with the shellsand the mold sectors can be termed semi-rigid.

The present invention makes it possible to combine the advantages of amanufacturing process without shaping with the advantages of a moldingwith a mold having fewer parts since without the inner core, andtherefore without having to construct a mechanism for removing and againmounting such an inner core. All the elements described in the presentspecification have been given in order to provide a completeillustration of the invention, without, of course, it being necessary touse them simultaneously.

We claim:
 1. A transportable tire manufacturing module for building a tire outside a mold and vulcanizing a tire within a mold, said module comprising an inflatable and deflatable flexible bladder having an outer tire building and molding surface, a bladder holder having relatively movable plates for anchoring the bladder along opposite edges of the bladder, the plates being separated to facilitate the removal of the vulcanized tire from the module, a central hub receiving means in one of the plates of the bladder holder for the rotation of the module during the deposit of products on the bladder, actuatable locking means between the relatively movable plates which are accessible and releasable through the hub receiving means for holding the plates together during the building and vulcanization of the tire and permitting them to be separated for the removal of the vulcanized tire from the module, the holder and bladder defining an inflatable enclosure which, in inflated condition, has a toroidal shape which serves as an inner reference surface for building and vulcanizing a tire, sealing means between the plates when the plates are held together, valve means in the holder for introducing and discharging an inflation medium into and from the enclosure for inflating and deflating the bladder, the enclosure being adapted to contain a heated fluid during vulcanization, at least one rigid wall mounted on one of the plates adjacent to the outside of the bladder in the region of the inner periphery of the bladder adjacent the anchored edges thereof, said rigid wall being retractable radially and inwardly over the bladder to permit removal of the tire from the module after vulcanization and moving outwardly when the bladder is inflated to provide a circumferentially continuous supporting surface for building the inner side wall of the bead portion of the tire during the assembling of the tire and a molding surface for the inner surface of the bead portion of the tire during vulcanization, and axially opposite coupling parts on the module adapted to be coupled with releasable grasping means and in which the said wall is formed by an assembly of members which arc articulated on said plate, around an axis perpendicular to a radial plane, forming a continuous inner convex surface engagable with the bladder and outer concave surface on which the inner surface of the bead portion of the tire is built and molded when the bladder is inflated, the members being arranged alternately one below the other in retracted position.
 2. A module as set forth in claim 1 in which the movement of said members from the retracted position to the outward position is controlled by the inflation of said bladder and the reverse movement is permitted by the deflation of the bladder.
 3. A module as set forth in claim 2 in which the assembly includes an even number of members distributed in two groups, the circumferentially adjacent members belonging to different groups, a movement of the members into retracted position orienting the members axially towards the center of the module.
 4. A module as set forth in claim 1 including a stop for limiting the rotation of the members by the inflation of the bladder. 